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Novel corrosion inhibiting coating technology for the protection of aluminum alloys

Peter Visser

15 June 2011

AkzoNobel Aerospace Coatings

Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011

2

Introduction

The Aerospace industry is relying on chromatedtechnologies for many years

Strong drive for Chromate replacement

• Legislation (REACH)

• Health Safety and environmental concerns

• Sustainability and eco-efficient developments

Chromated technology is still being used to achieve key performance characteristics.


3

Are chromates still needed for key performance using chrome free coating technology?


4

Pitting CorrosionPitting Corrosion

Fast development of long and highdensity filiform corrosion

Fast development of long and highdensity filiform corrosion

Rapid development of corrosion Early formation of blisters along scribesExcessive formation of corrosion products

Rapid development of corrosion Early formation of blisters along scribesExcessive formation of corrosion products

The Challenge:Development of total chrome free coating solutions.


5

The Challenge:Development of total chrome free coating solutions.

State of the Art corrosion inhibitorsmake it very difficult to comply withthe long term corrosion requirementsof the industry.

• Too low or high Solubility

• Compatibility with coatings system

• Insufficient passivation

• Specific activity

• Inconsistent performance


6

New approaches are needed to provide

total chrome free coating solutions


7

New Approach total chrome free TechnologyMagnesium Rich Primer Technology

Technology based on Magnesium metal particles as corrosion inhibitor

The anti-corrosive propertiesof this coatings is basedon two different mechanisms:

Cathodic protectionprovided by Mg metal powder

Barrier protectionprovided by the binder andprecipitated Mg oxides (1)

Significant departure from traditionalmethods and mechanisms ofcorrosion protection in aerospaceindustry

100µm100µm100µm

0 2000 4000 6000T, s

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

OCP

, V

Extent of Cathodic ProtectionExtent of Cathodic ProtectionDeveloped in MgDeveloped in Mg--rich Primersrich Primers

AA2024

AA7075

0 2000 4000 6000T, s

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

OCP

, V


AA2024

AA7075

Non-coated Bare

Coated Bare

Magnesium

0 2000 4000 6000T, s

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

OCP

, V


AA2024

AA7075

0 2000 4000 6000T, s

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

OCP

, V


AA2024

AA7075

Non-coated Bare

Coated Bare

Magnesium


8

Magnesium Rich Primer technology combined with appropriate chrome free pretreatments and topcoats provide a fully chromate-free system which exceeds the corrosion capabilities of commercial and military standard products.

Filiform corrosion development (EN3665) (2024 T3 Unclad, Scotch Brite solvent cleaned)

012345678

0 500 1000 1500 2000Hours

max

. len

gth

filam

ent

(mm

)

chromate inhibitor MGRP

2000h NSS (ASTM B-117)-Full chromate stack-up Total Chrome free System MgRP

New Approach total chrome free TechnologyMagnesium Rich Primer Technology


9

New Chrome free coating technology

A new patented chrome free coatings technology has been developed providing:

• Active inhibition of filiform corrosion

• Fast and effective passivation mechanism in Neutral Salt Spray

• Robust performance over clad and unclad substrates.

• Total chrome free coating systems meeting Aerospace requirements

• Universal Use

• Independent from resin technology


10

Meeting the Challenge

Long term corrosion protection

in

Neutral Salt Spray and Filiform corrosion


11

Meeting the challenge:Resistance to Filiform Corrosion.Focus of new chrome free developments:

• Low corrosion rate

• Reduced distribution of corrosion (morphology & area)

Process of Filiform corrosion

Filiform corrosion development (EN3665) (2024 T3 Unclad TSA)

0

1

2

3

4

5

6

0 500 1000 1500 2000

Time (h)

max

. len

gth

filam

ent (

mm

)

inhibitor 1inhibitor 2inhibitor 3inhibitor 4New technologychromate

Initiation/activation Nucleation Growth /Propagation

Nucleation Growth

Growth


12

Meeting the challenge:Neutral Salt Spray (ASTM B-117)

Development strategy to meet the challenge of long term Neutral Salt Spray exposure:

• Corrosion inhibitor with leaching properties

• Fast and effective passivation mechanism in the scribe

• Irreversible nature passivation layer.

• Maintain coating integrity


13

The corrosion performance of the new chrome free coatingtechnology has been studied in a High Solids coatingsystem suitable for Aerospace applications

• Comparison against chrome free inhibitors and Chromates• Primer / top coat systems• Currently used chrome free pretreatments

Meeting the challenge with chrome free coating technology


14

Active inhibition of Filiform corrosion (EN3665)


15

Example 1: Filiform performance on 2024 T3 UncladPretreatment: Scotch Brited / solvent cleaned

The New Technology provides:

• Lower corrosion rate

• Shorter filamentsNew Technology ChromateNew Technology ChromateTechnology Chromate

2000 h Filiform2024 T3 Unclad SB/SC

Filiform corrosion development (EN3665) (2024 T3 Unclad Scotch Brited/ Solvent cleaned)

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000Exposure time (h)

max

. len

gth

filam

ent (

mm

)

inhibitor 1

inhibitor 2

inhibitor 3

inhibitor 4

New technology

chromate


16

New Technology provides:


• Shorter filaments

Example 2: Development Filiform Corrosion(EN 3665) 2024 T3 Clad- Solgel

Filiform corrosion development (EN3665)(2024 T3 Clad- Solgel)

0

1

2

3

4

5

6

7

8

0 500 1000 1500 2000

Exposure Time (h)

Max

. len

gth

filifo

rm (m

m)

Inhibitor 1

Inhibitor 2

Inhibitor 3

Inhibitor 4

New Technology

Chromate

2000 h Filiform 2024 T3 Clad – Sol gel

Chromate New Technology






17

Example 3: Development Filiform Corrosion(EN 3665) 2024 T3 UnClad-TSA

• New Technology: Lower Corrosion rate and shorter filaments

Filiform corrosion development (EN3665) (2024 T3 Unclad TSA)

0

1

2

3

4

5

6

0 500 1000 1500 2000

Time (h)

max

. len

gth

filam

ent (

mm

)

inhibitor 1inhibitor 2inhibitor 3inhibitor 4New technologychromate


18

Using Imaging techniques for the development of Chrome free technologyAnalysis and rating of coating systems during and after exposure.

• Applicable to:

• Filiform corrosion

• Neutral Salt Spray

•Providing data:

• Creep from Scribe

• Affected area

• Type of corrosion

A B A BDistribution Filiform corrosion

0%

20%

40%

60%

80%

100%

0.0 5.0 10.0 15.0

Filiform corrosion length (mm)

Freq

uenc

ySample A Sample B

Distribution Creep from scribe

0%

20%

40%

60%

80%

100%

0.0 2.0 4.0 6.0 8.0 10.0

distance from scratch in mmfre

quen

cysample A sample B

A B


19

New Technology provides:

• Shorter filaments

• Reduced corrosion area

Example 3: Filiform performance on 2024 T3 Unclad-TSAImaging analysis after 2000 h exposure

Inhibitor 1 Inhibitor 2 Inhibitor 3 Inhibitor 4 New Technology Chromate

Distribut ion filiform corrosion (EN 3665)2024 T3 Unclad-TSA

0%

20%

40%

60%

80%

100%

0.0 2.0 4.0 6.0 8.0distance from scratch in mm

filifo

rm le

ngth

freq

uenc

y inhibitor-1inhibitor-2inhibitor-3inhibitor-4NewTechChromate

Maximum Length Filiform Corrosion 2000 h (2024 T3 Unclad-TSA)

0.01.02.03.04.05.06.07.08.09.0

10.0

max left max right

max

. len

gth

(mm inhi bitor-1

inhi bitor-2inhi bitor-3inhi bitor-4NewTech

C hromate

Total Corrosion area after 2000 h Filiform(EN 3665)2024 T3 Unclad-TSA

0

50

100

150

200

total

area

in m

m^2

inhibitor-1inhibitor-2inhibitor-3inhibitor-4NewTechChrom ate


20

Summary on filiform corrosion

The new Technology provides activeFiliform corrosion inhibition:

• Shorter Filaments


• low affected area

• Long term corrosion protection

• Activity on mutiple substrates

•


21

Fast and Effective Protection of the Scribe

In Neutral Salt Spray (ASTM B-117)


22

3000 h exposure 2024 T3 Unclad – TSA

New Technology: Lower corrosion rateLess creep from scribe

Evolution Creep from scribe in NSS (ASTM B-117)(2024 T3 Unclad - TSA)

0

0.5

1

1.5

2

2.5

0 500 1000 1500 2000 2500 3000

Time (h)

Cre

ep fr

om s

crib

e( m

m)

inhibitor 1inhibitor 2inhibitor 3inhibitor 4new technologychromate

Corrosion distribution after 3000 h NSS (ASTM B-117)(2024 T3 Unclad - TSA)

0

0.5

1

1.5

2

2.5

3

3.5

inhibitor 1 inhibitor 2 inhibitor 3 inhibitor 4 NewTechnology

Chromate

max

. cre

ep fr

om s

crib

e( m

m)

0

20

40

60

80

no. o

f cor

rosi

on s

ites

max Creep from scribe no. Of corrosion sites

Low number of corrosion sites

Example 4: Corrosion Development in NSS (ASTM B-117)2024 T3 UnClad-TSA


23

Example 5: Corrosion development in NSS (ASTM B-117)2024 T3 Clad Solgel

New Technology:

Less creep from scribe

Evolution Creep from scribe in NSS (ASTM B-117)(2024 T3 Clad - Solgel)

0

1

2

3

4

5

6

7

0 500 1000 1500 2000

Time (h)

Max

cre

ep fr

om s

crib

e (m

m)

Inhibitor 1Inhibitor 2Inhibitor 3Inhibitor 4New Technologychromate


24

Example 5: Corrosion development in NSS (ASTM B-117)2024 T3 Clad Solgel

New Technology: Clean ScribesLess creep from scribeLow number of corrosion sites

Chromate New Technology Inhibitor 4

2024 T3 Clad Sol gel, 2000 h2000 h Neutral Salt Spray (ASTM B-117)


25

Distribution Creep from scribe corrosion length2024 T3 Clad-Solgel NSS 2000h

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.0 1.0 2.0 3.0 4.0 5.0

distance from scratch in mm

freq

uenc

yinhibitor 1inhibitor 2inhibitor 3inhibitor 4New Technologychromates


2000 h Neutral Salt Spray (ASTM B-117)2024 T3 Clad Solgel, 2000 h


2000 h Neutral Salt Spray (ASTM B-117)2024 T3 Clad Solgel, 2000 h New Technology provides:

• Less creep from scribe• Low number of corrosion sites• Low corrosion affected area

Example 5: Imaging analysis after2000 h NSS (ASTM B-117) 2024 T3 Clad Solgel

Corrosion Distribution(after 2000 h NSS (ASTM B-117)

050

100150200

250300350400450

number of sites total area

inhibitor 1inhibitor 2inhibitor 3inhibitor 4New TechnologyChromate

Corrosion Distribution(after 2000 h NSS (ASTM B-117)

050

100150200

250300350400450

number of sites total area

inhibitor 1inhibitor 2inhibitor 3inhibitor 4New TechnologyChromate


26

Chromate inhibitor

New chrome free technology

State of the Art chrome free technology

The New Technology provides fast and effective protection of the scribe:

• Bright, shiny and clean scribes.Scribe appearance

500 h NSS (ASTM B-117) 2024 T3 unclad

Fast and Effective Protection of the Scribe


27

Scanning Electron Microscopic analysis :

•Evidence for protective layer in the scribe.

2024 T3 Clad after

1000 h NSS (ASTM B-117)

Fast and Effective Protection of the ScribeScribe analysis after 1000 hours exposure


28

Using White Light Interferometry for scribeanalysis

White Light Interferometry (WLI):

• Non-contact measurement of surface topography

Determining:

•Surface Roughness

•Surface Area


29

Scribe appearance using White Light Interferometry

500 h NSS (ASTM B-117) 2024 T3 unclad

Chromate inhibitor

New chrome free technology

State of the Art chrome free technology

Using White Light Interferometry for scribeanalysis


30

White Light InterferometryScribe analysis after Neutral Salt Spray (ASTM B-117)

New Technology State of the Art Chrome Free

Surface Roughness development in NSS (ASTM B-117)2024 T3 Unclad

250 h

500 h

1000 h


31


2024 T3 Unclad 1000h 2024 T3 Clad

Surface Roughness of Scribe (Ra)

0

1

2

3

4

5

250 h 500 h 1000 h 250 h 500 h 1000 h

2024 T3 Bare 2024 T3 Clad

Surfa

ce R

ough

ness

(Ra)

in u

m

Starte of the Art CFChromatedNew Technology

State of the Art CF

Chromated

New Technology


32

Prevention of pit corrosion is one of the largest challenges in long term Neutral Salt Spray exposure.


Chromate inhibitor

New Chrome Free Technology

State of the Art Chrome free

pit corrosion after 2000 h NSS (ASTM B-117)

2024 T3 unclad


33


Inhibitor 1 New TechnologyInhibitor 3 ChromateInhibitor 2

Surface Roughness and Pit corrosion 2024 T3 Unclad after 2000 h NSS (ASTM B-117)

Surface Roughness (Ra) after 2000 h NSS (ASTM B-117)

0123456

inhibitor 1 inhibitor 2 inhibitor 3 Chromate New TechnologySurf

ace

Rou

ghne

ss (R

a)

in u

m


34

Summary

During Neutral Salt Spray Exposure (ASTM B-117) the New Technology provides:

• Fast and effective protection of the scribe

• Reduced creep from scribe

• Low number of corrosion sites

• Less pit corrosion

• Long term corrosion protection


35

Conclusion

The New Chrome Free Technology provides:

• Proven corrosion protection in multiple corrosion tests.

• Fast and effective passivation of scribe

• Excellent Filiform corrosion inhibition

• Significant less corrosion

• Expected long term performance

• Active on multiple substrates

• Total chrome free technology

• Universal performance

• Fully Health Safety and Environmentally compliant technology


36

A New Total Chrome Free Coating Solution

for the protection of aluminium alloys